Conventionally, inspection of grid beams forming top guide structures in boiling water reactors are performed by an In-Vessel Visual Inspection (IVVI) Level II inspector and camera handler hanging a camera handled by its cable from a refuel bridge or an auxiliary bridge. This method may be time consuming, may expend too much dose and may not provide stability necessary for such an inspection.
U.S. Pat. No. 5,692,024 discloses an underwater crawler vehicle that rides on the top edges of two parallel grid members of a top guide structure and positions an inspection system to enable volumetric inspection of each grid member. The inspection system includes an ultrasonic inspection instrument to inspect the top guide structure.